FLOOD01117

• Designation Number: 219
• County: Arapahoe
• Community: Littleton
• Stream Name: Upper Slaughterhouse Gulch
• Title: Major Drainageway Planning - Upper Slaughterhouse Gulch
• Date: 3/1/1983
• Designation Date: 7/1/1983
• Floodplain - Doc Type: Floodplain Report/Masterplan

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CHAPTER V - MAJOR DRAINAGEWAY IMPROVEMENTS

The alternative selected by the sponsoring agencies also included the

direction to investigate lowering the South Delaware Street centerline crown

from West Powers Avenue to West Powers Place to provide a more effecient over-

flow for floods larger than the 5-year. The lowering of the street crown was

found to increase the capacity of the system to the lO-year, but not enought

to provide an increase in protection without the 5-year storm sewer. To carry

the residual 50-year flood peaks (Q approximately 420 cfs), the street would

require lowering in excess of 2-feet. The parking requirements along the east

side as well as the existing utilities in Delaware Street preclude such an

improvement.

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A brief description of the selected major drainageway improvements was
presented in the summary table in the Synopsis. A detailed description of the
alternatives is presented in this chapter. The design criteria used for the
improvements and a discussion of the master plan drawings is also presented in
this chapter.

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A. Selected Alternative

Also included in the Phase-A recommended alternatives, were improvements
to the Powers Park detention area. Further analysis showed that substantial
improvements were not required. With the Caley detention pond, Powers Park
will essentially contain the 5~year flood with minimal flow over the emergency
spillway. To provide totalS-year storm containment, the spillway would have
to be raised by 2-feet. This would require regrading the crest which would
provide only a minimal flood cOntrol improvement downstream. Therefore, the only
improvements recommended for Powers Park consist of a continued maintenance pro-
gram and conEtruction of a trickle channel through the park area.

The recommended alternatives in the Phase-A report were reviewed by the

participating agencies. In addition, a legal review of the Phase-A report was

conducted and the legal opinion is included in Appendix-B. The notice-to-proceed

for Phase-B included revisions to the recommended alternatives as well as general

administrative policies covering the entire study area. The notice-to-proceed letter

and the "selected Phase-B plan" are included in Appendix-A. The selected plan ~s

shown in schematic form on Figure V-I. A discussion of the alternative specifics

for each reach is presented below:

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l. REACH-A (Powers Park to City Limits)
Reach-A damages consist of inundation of the residential and commercial
areas adjacent to the drainageway. The flooding is caused by an inadequate
existing storm sewer system along the entire reach. The problems are also
compounded by a sump condition at Broadmoor Drive behind the pink Flamingo
Apartments. Flooding in this reach causes structure, content and utility
damage, interrupted traffic, and creates a potential life and safety hazard.

2. REACH-B (City Limits to Grant Street)
The recommended plan in the Phase-A report consisted of status quo and flood-
plain zoning due to the lack of development and damages. During the Phase-B
preliminary design, it was determined that a portion of the reach required a
storm sewer due to the topographic constraints. In addition to the sewer, a
5-year open channel has been planned to carry the design flows for the remainder
of the reach.

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3. REACH-C (Grant Street to Caley Avenue)
The selected alternative for Reach-C is construction of a 5-year storm
sewer along East Maplewood Drive up to South Pennsylvania Street then along
South Pennsylvania Street to Caley Avenue. A 5-year collector system east of
South Pennsylvania Street is also to be constructed to intercept the local
drainage along Clarkson Street. Problems in Reach-C are caused by inadequate
drainageway facilities resulting in the inundation of adjacent residences. Dam-
ages are mainly comprised of structure and content damage and interrupted taffic.
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The selected alternative in this reach consists of what will ultimately

be a 5-year storm sewer to eliminate the frequent storm flooding and reduce

the flooding from storms larger than the 5-year storm. The sizing of the

5-year storm sewer considers the affects of upstream detention above Caley

Avenue. Prior to construction of the Caley detention facility, the storm sewer

would affcrd protection approximately equal to that of a 2-year system.

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